This invention relates to a computer system having a thermal sensor to detect overheating and to allow system shutdown before unstable operating conditions occur, and more particularly to such a system wherein a dual voltage source is used to provide stabilization of a thermal sensor.
Computer systems use thermal sensors mounted in the CPU housing to determine when the system is operating outside its specified range. Usually these thermal sensors have a circuit which establishes a trip point at which an interrupt is signalled to the operating system of the CPU to take appropriate action, e.g., to begin an orderly shutdown of the system when a certain temperature is reached. In this manner, all files can be closed, data written to permanent storage (hard disk), and any pending tasks or applications properly closed. A lower set point may merely generate a message to a system administrator to indicate that overheating is approaching so that action can be taken. In any event, the set points or trip points must be closely controlled so that unnecessary overheating conditions are not signalled.
Commercially-available, relatively inexpensive, thermal sensors are characterized in that the outputs vary in response to supply voltage (or current) as well as with temperature. The result of this voltage sensitivity is that the thermal sensor circuitry can report overheating when the actual temperature is within tolerable limits. This causes unnecessary shutdown of the system, and as a consequence the maintenance cost and system downtime are needlessly affected.
In one example, a computer system may specify the power supply as producing operating voltages for the computer that are at nominal levels such as 5V or 12V, but these may vary +/-5% and still be within operating tolerance. But if the temperature inside the CPU housing is specified to be a maximum of 70.degree. C., and if the thermal sensor which is used has an output that varies with voltage supply level, then the overheating shutdown may be tripped at 66.5.degree. C. This is unnecessary and wasteful, since the computer system may be able to operate continuously at a high performance level at this temperature, with no unwanted effects.